當前的射頻識別(RFID)標簽測試方法對大量的倉庫和貨架上的標簽是一個負擔,因為當前的測試方法需要對每一個標簽獨立調諧,因此測試流水線化可以獲得更快的原型設計時間,喬治亞工學院的工程師們最近設計了一種新的測試機,可以在新標簽芯片仿真的時候同時測試數百個RFID標簽。

喬治亞電氣和計算機學校的Gregory Durgin教授宣稱“我們設計了一種超靈活的系統,能夠允許改變調制方法,載波頻率,射頻標簽配置,天線類型?D?D任何可以使工程師獲得更大范圍和靈活性的系統性能參數,一些公司已與我們合作運用這一測試機來測試新的天線標簽,并利用這些新的傳感器性能來刷新現有的RFID標簽。”

RFID標簽運用十分廣泛,從存貨管理到收費系統到護照識別再到行李跟蹤。而大部分的標簽都只是被動式的,包含一個芯片,一個能夠接收無信電信號的天線給附近的讀卡機提供身份識別。

RFID標簽測試的最大的問題是測試量?D?D倉庫和商店貨架往往包含讀卡機范圍內的上百種標簽,很多標簽隱藏在其他標簽的后面,當這些標簽都在讀卡機范圍內的時候,通常的協議是先響應最強信號的標簽,識別后讓它休眠再處理下一個最強信號,這一系列過程很耗時。

然而,喬治亞測試機運用了一種防干擾系統能夠同時傳輸若干獨立信號,這個系統允許256個標簽同時被訪問,而不是要求讀卡機依次訪問各個標簽,喬治亞測試機可以與400平方英尺內的RFID標簽通信,同時收集標簽信息,該系統還能實時追蹤它們的信號強度。

Durgin 說“我們有一個自動機械配置系統可以自動調整標簽的距離,這樣我們可以研究空間變化和鏈接衰減的特征。”

用新天線設計測試RFID標簽也有一個新問題,需要新的RFID標簽的物理原型用來測試天線,往往也需要昂貴的ASIC設計。為解決這一問題,喬治亞的團隊發明了一種替代品來替代新標簽設計里的ASIC,從而使這種新的天線能夠很快被測試。

Durgin 說“我們用傳統的發收器硬件來產生和接收任意波形,這樣我們能迅速的測試獨立的天線配置和若干天線,而不需要為每一個實驗創立新的標簽。同時,我們用定制的微波電路來模擬ASIC,用它可以模擬任意載頻和任意調制方法的真實的RFID標簽,甚至是全新的設計”

目前測試機僅限于915MHz的測試,這也是被動式RFID應用的最常用的頻率,但目前已被更新至2.4- 5.7-GHz。這些更高的頻率將使標簽可以用更小的天線實現更廣泛的操作范圍。

喬治亞RFID測試機由國家科學基金會贊助。喬治亞工學院工程學研究生Anil Rohatgi 和 Joshua Griffin主導這項研究。

翻頁查看英文原文:

Test bed streamlines RFID development

RFID tags flooding warehouses and product shelves tax current testing methods, which separately tune into each tag. To streamline testing while enabling rapid prototyping of new designs, Georgia Institute of Technology engineers have crafted a new test bed they say is capable of simultaneously testing hundreds of RFID tags while emulating the chip in a new tag design.

"We have designed a super-flexible system that allows us to vary modulation scheme, carrier frequency, RF tag configuration, antenna types -- anything an engineer can dream up for making these systems perform with greater range and reliability," claimed professor Gregory Durgin at Georgia Tech's School of Electrical and Computer Engineering. "Companies have already -partnered with us to use the testbed to test new tag antennas, and to retrofit existing RFID tags with new sensor capabilities."

RFID tags are used for everything from inventory management to toll collection to passport identification to tracking luggage. Most tags are passive, including a chip and an antenna that absorbs a radio signal to backscatter its identity to a nearby reader.

The biggest problem with testing RFID tags is the sheer volume--warehouses and store shelves often contain hundreds of tags within range of a reader, many hidden behind other tags. When multiple tags are within range of a reader, the usual protocol is to interrogate the tag with the strongest signal, then put it to sleep and proceed on to the next strongest signal. That serial process can be time consuming.

Instead, the Georgia Tech test bed uses an anti-collision system capable of transmitting multiple, unique signals. The system allows up to 256 tags to be interrogated simultaneously. Instead of requiring readers to be within about a foot of tags, the Georgia Tech test bed can communicate with RFID tags within 400 square feet of the tester. Along with collecting tag information, the system can also track their signal strength in real time.

"We also have a robotic positioning system that drags tags through space so that we can study spatial variability and characterize link fading," said Durgin.

Testing RFID tags with new antenna designs is also a problem. A physical prototype of the new RFID tag must be built to test the antenna, often involving the costly ASIC fabrication. To solve the problem, the Georgia Tech team created an emulator that substitutes for the ASIC in a new tag design, thus allowing new antennas to be quickly prototyped and tested.

"We use custom transmitter and receiver hardware to generate and receive an arbitrary waveform of our own design so we can rapidly test unique antenna configurations and multiple antennas without actually constructing new tags for each experiment," said Durgin. "Instead, we use our custom microwave circuits to emulate the presence of an ASIC--it just clips onto the antenna. With it, we can emulate realistic RFID tags at any carrier frequency with any modulation scheme--even new ones of our own design."

The current test bed is limited to measurements at 915 MHz, the most common frequency for backscatter RFID applications, but it is currently being upgraded to test antennas at frequencies of 2.4- and 5.7-GHz. These higher frequencies will enable tags to operate over wider ranges while using smaller antennas.

The Georgia Tech RFID test bed was funded by the National Science Foundation. Georgia Tech engineering graduate students Anil Rohatgi and Joshua Griffin conducted the research.